Cooling fluid widely used at present is low in price, has good in anti-corrosive performance and the raw materials are easily available. However, it does not have good stability due to the presence of compositions of silicates and 2-mercaptobenzothiazole.
Silicate is a kind of special efficient corrosion-inhibiting agent for aluminum and alloys thereof. It has certain protective capability for steel and iron, as well as non-ferrous metals. It not only possesses buffer function, but also is extremely cheap. In the past several decades, it has been extensively applied in various fields for protecting from corrosion. However, the main problem of silicates in the course of application is that their stability decreases after they have been stored or used for a period of time and a gel-like precipitation readily separates. As a result, their inhibition capability is decreased. Moreover, the said gel-like precipitation may block-up the water channels of the engine and also adhere to the surface of the radiator during operation so as to reduce the heat transfer effect and make engine overheat. The instability of the silicates is caused by precipitated silicate gel and the precipitation of the reaction products of silicate with calcium, magnesium ions etc. contained in hard water. The latter can be dealt with by controlling the hardness of the water. However, the situation is comparatively complicated for silicate gel. In general, it is believed that the silicates aggregate per se or conduct reaction to form particulates. The particles agglomerate to form branched chain and then network structures, and finally gel is separated. With the rapidly development of the auto engine industry, engine power is increasing. In order to reduce windage coefficient, a streamlined shape is generally designed. It makes the sizes of the radiator and water tank smaller and smaller. Thereby, the heat-load of the engine is gradually increased. For the purpose of reducing the weight of the vehicles bodies and increasing economy of the fuel, not only a great amount of aluminum alloy is used for engine's cooling system, but also the other parts of the engines are gradually aluminum-metallized. Now an all-aluminum engine has been put on market. Research on the protection from corrosion of aluminum is now becoming a key importance in various countries.
2-mercaptobenzothiazole is an especially efficient inhibiting agent for copper or alloys thereof, and easily conducts a photosensitive reaction to produce precipitates—a factor influencing stability. Therefore, it is a very important object to increase the stability of cooling fluid for the engine.